1. Field of the Invention
The present invention relates generally to a method and apparatus for measuring a thickness of a metal layer. More particularly, the present invention relates to a method and apparatus for measuring a thickness of a metal layer formed on a semiconductor substrate using a laser beam irradiated onto a surface of the metal layer.
A claim of priority is made to Korean Patent Application No. 2004-62816 filed on Aug. 10, 2004, the disclosure of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
The performance of semiconductor devices is determined, at least in part, by the size and density of processing elements formed on the devices. For example, semiconductor devices with smaller, more densely formed processing elements generally achieve higher performance (e.g., throughput, data access speed, clock rate, etc.) than semiconductor devices having larger, less densely formed processing elements. Accordingly, considerable effort has been invested in developing methods of manufacturing semiconductor devices with smaller, more densely formed processing elements.
The manufacture of modern semiconductor devices typically includes several processing steps including various chemical and/or photographic processing steps, as examples. In the processing steps, various layers are typically formed on a semiconductor substrate and then etched to form processing elements.
In order to decrease the size (i.e., the critical dimension) of the processing elements, it is generally necessary to decrease the thickness of the layers formed on a semiconductor substrate. As the thickness of the layers decreases, an aspect ratio (i.e., width/height) of patterns formed on the substrate tends to increase as well. In addition, as the thickness of the layers decreases, inspection processes used to evaluate characteristics of the layers or patterns formed thereon become increasingly important.
Various devices such as a scanning electron microscope (SEM), a transmission electron microscope (TEM), a secondary ion mass spectrometer (SIMS), an X-ray fluorescence spectroscope (XRF) and an X-ray reflectometer (XRR) have been used to perform inspections on thin layers in the past. For example, U.S. Pat. No. 4,510,573 discloses an XRF, and U.S. Pat. No. 5,778,039 discloses a method and apparatus for inspecting a surface of a semiconductor substrate using the XRF. U.S. Pat. No. 6,453,006 discloses an XRR.
As explained previously, semiconductor devices are typically crated by forming several layers on a semiconductor substrate. In order to avoid producing defects in the semiconductor device, certain characteristics of the layers such as uniformity of doping concentration and thickness need to be carefully regulated. Accordingly, inspection processes are commonly performed to detect defects, irregularities, or non-uniformities on surfaces of the layers.
A titanium nitride layer is commonly utilized as a barrier layer in forming electrical devices such as transistors or capacitors or in forming a metal wiring. The thickness of the titanium nitride layer is generally very small. For example, in a flash memory device, the titanium nitride layer is formed to an even thickness of about 50 Å.
Unfortunately conventional inspection methods and apparatuses fail to properly inspect very thin layers because they lack the required resolution. In other words, they are not precise enough. Accordingly, new inspection methods and apparatuses are needed. In particular, improved methods and apparatuses are needed to inspect metal layers whose thickness is less than that of a dielectric layer formed on the semiconductor substrate.